1. Field of the Invention
Embodiments of the invention relate to a display device. More particularly, embodiments of the invention relate to a source driver, a liquid crystal display (LCD) device, and a method of driving a data line of an LCD.
This U.S. non-provisional application patent application claims priority under 35 USC §119 of Korean Patent Application No. 2006-51781 filed on Jun. 9, 2006 the entire contents of which are hereby incorporated by reference.
2. Discussion of Related Art
Liquid crystal display (LCD) devices are widely used in imaging devices such as digital video cameras, digital still cameras, computer monitors and television displays. LCDs are also used in portable electronic devices such as cellular phones, and personal digital assistants (PDAS) to display images and/or text information. An LCD device may display an image by using optical anisotropy of liquid crystal. The LCD device has advantages such as thinness, small size, low power consumption and high resolution to be developed as a flat display device which replaces a cathode ray tube (CRT). However, the LCD device has relatively low quality with respect to moving images as compared to conventional CRTs.
Generally, a response time of an LCD device is longer than a frame display period (about 16.7 ms) due to viscosity which is an elastic force of a liquid crystal molecule. The response time corresponds to a time from when an electric field is applied to the liquid crystal molecules to when a predetermined transmittance is obtained by changing an arrangement of the liquid crystal molecules. The long response time may not influence an image or a moving image when a luminance change of an image is small from frame to frame, but may compromise a moving image in which the luminance change of the image is large from frame to frame. In the latter instance, the actual luminance of pixels may not reach a desirable level and then may be changed according to a signal associated with the next frame. Thus, degradation of image quality such as image contrast may result.
An LCD device is driven using a hold-type method where charges accumulated in the liquid crystal molecules due to the electric field are maintained at a high ratio until the next electric field is applied. Thus, each pixel of the LCD device maintains emission until the signal of the next frame is applied. When images representing moving objects are displayed from frame to frame, an afterimage of the object of the previous frame remains when the next frame image is processed. Accordingly, motion blurring may result where the object is not moving, but appears to be stretched.
An impulsive-type driving method which inserts a black or white screen for a short time is one way to solve this problem. The impulsive-type driving method includes an impulsive emission type and a cyclic resetting type. In the impulsive emission type, a backlight is turned off with a predetermined period so that the whole screen becomes black. In the cyclic resetting type, a black data voltage or a white data voltage is applied to the pixels with a predetermined period along with a normal data voltage.
According to flexible black data insertion technology, a frame frequency is twice a conventional frequency (120 Hz) and a frame time is half of a conventional time (8.3 ms). In addition, a maximum level of 50% of black data is inserted according to a luminance to improve the moving image quality. In particular, in the hold-type driving method data in one frame is divided into two frames at 60 Hz. An image, lighter than an original image, is allocated to one frame and a darker image including black data is allocated to the other frame. Thus, the two frames have the same luminance by integrating the two frames by time. However, this method requires high power consumption due to high operation speed. As a result, the technology is not applicable for small and medium-size display devices used in cellular phones and similar devices. In addition, it may be required to insert black data at different frame rates depending on the type of display panel used in order to prevent afterimages due to individual panel characteristics.